Vacuum processing systems for processing 100 mm, 200 mm, 300 mm or other diameter wafers are generally known. An example of a typical vacuum processing system 10 is shown in FIG. 1a. The system 10 typically has a centralized transfer chamber 12 mounted on a monolith platform (not shown). The transfer chamber 12 is the center of activity for the movement of wafers being processed in the system. One or more process chambers 14 attach to the transfer chamber 12 at valves through which the wafers are passed by a robot 16 in the transfer chamber 12. The valves are selectively opened and closed to isolate the process chambers 14 from the transfer chamber 12 while wafers are being processed in the process chamber 14. Physically, the process chambers 14 are either supported by the transfer chamber 12 and its platform or are supported on their own platform. Inside the system 10, the transfer chamber 12 is typically held at a constant vacuum; whereas, the process chambers 14 may be pumped to a greater vacuum for performing their respective processes. Afterward, the chamber pressure must be returned to the level in the transfer chamber 12 before opening the valve to permit access between the chambers.
Access to the transfer chamber for wafers from the exterior of the system, or from the manufacturing facility, is typically through one or more load lock chambers. The load lock chambers cycle between the pressure level of the ambient environment and the pressure level in the transfer chamber in order for the wafers to be passed therebetween, so the load lock chambers transition the wafers between the atmospheric pressure of a very clean environment to the vacuum of the transfer chamber. Load lock chambers typically have a large volume holding several wafers, from about thirteen to about twenty five wafers. The wafers are stacked vertically in a wafer cassette with a space between each wafer permitting a robot blade to reach under a wafer to remove the wafer. Thus, a fairly large volume is being transitioned between the atmospheric pressure and the vacuum pressure, which takes about four minutes. During the time to perform this transition, no process is being performed on the wafers.
The load lock chambers may open to the ambient environment for an operator to load a wafer cassette, or pod, thereinto or the load lock chambers may attach to a mini-environment which transfers wafers in a very clean environment at atmospheric pressure from wafer pods to the load lock chambers. The mini-environment also has a wafer orienter or aligner for aligning the wafer so that the wafer is properly oriented in the load lock chamber.
Some common transfer chambers have four to six facets to mount process chambers and load lock chambers. For a six-faceted transfer chamber, typically two of the facets are designated for load lock chambers, and the other four facets are designated for process chambers. The process chambers include rapid thermal processing (RTP) chambers, physical vapor deposition (PVD) chambers, chemical vapor deposition (CVD) chambers, etch chambers, etc. The productivity of a vacuum processing system is increased when more process chambers are mounted to the transfer chamber because more wafers can be processed at a given time. Additionally, less space is required in the manufacturing facility to process a certain number of wafers if the productivity of the system is maximized.
Some of the processes performed by the process chambers require that the wafers processed therein be pre-processed or post-processed before or after performing the primary process in a process chamber. For example, a process may require that a wafer be pre-heated before performance of the primary process, thus preparing the wafer for the primary process, so that the primary process proceeds more quickly or efficiently. In a second example, a process may require that a wafer be heated after performance of the process, such as a spin-on-glass process that coats the wafer with a liquid glass material that must be cured following deposition by heat-treating the wafer at elevated temperatures. In yet another example, a process may require that a wafer be cooled after performance of the process, so that the wafer is not too hot to handle or so that the wafer is not so hot that dopants or other material in or on the wafer diffuse through the wafer thereby compromising the integrity of the devices formed in or on the wafer.
For such processes, the vacuum processing system typically provides a processing element, such as a wafer heater or wafer cooler, in a location separate from the process chamber to perform the pre-processing or post-processing process on the wafer, so that the wafer spends as little time as possible inside the process chamber, and so that the process chamber does not have to incorporate the extra equipment required to perform these extra processing steps. For example, in the vacuum processing system 100 shown in FIG. 1, and described more fully in the detailed description of a preferred embodiment below, the transfer chamber 102 has four facets 106 for mounting process chambers 104 and two facets 112 for mounting load lock chambers 108. One or more of the facets 106 of the system, however, mount a pre-processing or post-processing chamber such as a cool-down chamber to cool a wafer after a process and/or a heating chamber to heat the wafer before or after a process. This separation of functions permits the system to perform tasks in parallel, so while a wafer is undergoing the pre-processing or post-processing step, another wafer is undergoing the primary processing step. However, the total throughput of the system 100 is reduced since the system 100 has fewer process chambers 104 for performing the primary processing of the wafers.
In order to perform the pre-processing or post-processing processes, the vacuum system 100 maneuvers a wafer through a series of steps prior to transferring the wafer to a process chamber 104 for performance of the primary process. Typically, these steps are performed by the transfer chamber 102 and an attached pre-processing or post-processing chamber. For example, after a load lock chamber 108 transitions a cassette of wafers to the vacuum level of the transfer chamber 102, a robot in the transfer chamber 102 moves the wafers, one at a time, to a process chamber 104 or a pre-processing chamber. After a wafer has been pre-processed, such as heated to an appropriate temperature, the robot moves the wafer to one of the process chambers 104 for primary processing. After the process chamber 104 completes its process on the wafer, the robot moves the wafer back to a load lock chamber 108 or to a post-processing chamber, such as a cool-down chamber. After the wafer has been post-processed, the robot moves the wafer to the load lock chamber 108. After all of the wafers in the cassette have been processed, the load lock chamber 108 transitions the wafers back to the ambient environment pressure level. The steps to move the wafers to and from the pre-processing and post-processing chambers add to the overall time required for processing a wafer through the vacuum processing system. The cost to manufacture an integrated circuit is typically directly related to the amount of time required to process the wafer; therefore, since a certain amount of time is required to perform the pre- and post-processing steps and to transition the load lock chamber, as discussed above, it is desirable to compress this time as much as possible.
Additionally, since an extra pre-processing or post-processing chamber occupies one of the locations on the transfer chamber that could be occupied by a process chamber, the productivity potential, or throughput, of the vacuum processing system is decreased. Therefore, in order for a manufacturing facility to achieve the same throughput as would be achieved if each system had the maximum number of process chambers and no extra chambers, the manufacturing facility would have to increase the number of systems in the facility, which translates to an increase in the amount of floor space dedicated to these systems. Thus, the manufacturing costs increase.
A need, therefore, exists for a vacuum processing system that uses the waiting time during the pressure transition in the load lock chambers to be more productive, reduces the time required for an individual wafer to be processed and decreases the amount of space required for the manufacturing facility.